Storing data sequentially in zones in a dispersed storage network

ABSTRACT

A method for execution by a storage unit in a dispersed storage network (DSN) includes selecting a storage zone of a memory device of the storage unit based on zone allocation parameters, and designating the selected storage zone as open for writes. A data slice is received via a network for storage. The data slice is written sequentially at a memory location of the one of storage zone based on determining that the storage zone is designated as open for writes. A pointer corresponding to the data slice that indicates the storage zone and the memory location is generated. A read request is received via the network from a requesting entity that indicates the data slice. The data slice is retrieved from the memory device based on the pointer, and is transmitted to the requesting entity.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION Technical Field of the Invention

This invention relates generally to computer networks and moreparticularly to dispersing error encoded data.

Description of Related Art

Computing devices are known to communicate data, process data, and/orstore data. Such computing devices range from wireless smart phones,laptops, tablets, personal computers (PC), work stations, and video gamedevices, to data centers that support millions of web searches, stocktrades, or on-line purchases every day. In general, a computing deviceincludes a central processing unit (CPU), a memory system, userinput/output interfaces, peripheral device interfaces, and aninterconnecting bus structure.

As is further known, a computer may effectively extend its CPU by using“cloud computing” to perform one or more computing functions (e.g., aservice, an application, an algorithm, an arithmetic logic function,etc.) on behalf of the computer. Further, for large services,applications, and/or functions, cloud computing may be performed bymultiple cloud computing resources in a distributed manner to improvethe response time for completion of the service, application, and/orfunction. For example, Hadoop is an open source software framework thatsupports distributed applications enabling application execution bythousands of computers.

In addition to cloud computing, a computer may use “cloud storage” aspart of its memory system. As is known, cloud storage enables a user,via its computer, to store files, applications, etc. on an Internetstorage system. The Internet storage system may include a RAID(redundant array of independent disks) system and/or a dispersed storagesystem that uses an error correction scheme to encode data for storage.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a schematic block diagram of an embodiment of a dispersed ordistributed storage network (DSN) in accordance with the presentinvention;

FIG. 2 is a schematic block diagram of an embodiment of a computing corein accordance with the present invention;

FIG. 3 is a schematic block diagram of an example of dispersed storageerror encoding of data in accordance with the present invention;

FIG. 4 is a schematic block diagram of a generic example of an errorencoding function in accordance with the present invention;

FIG. 5 is a schematic block diagram of a specific example of an errorencoding function in accordance with the present invention;

FIG. 6 is a schematic block diagram of an example of a slice name of anencoded data slice (EDS) in accordance with the present invention;

FIG. 7 is a schematic block diagram of an example of dispersed storageerror decoding of data in accordance with the present invention;

FIG. 8 is a schematic block diagram of a generic example of an errordecoding function in accordance with the present invention;

FIG. 9 is a schematic block diagram of an embodiment of a dispersed ordistributed storage network (DSN) in accordance with the presentinvention; and

FIG. 10 is a logic diagram of an example of a method of storingsequentially in zones in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram of an embodiment of a dispersed, ordistributed, storage network (DSN) 10 that includes a plurality ofcomputing devices 12-16, a managing unit 18, an integrity processingunit 20, and a DSN memory 22. The components of the DSN 10 are coupledto a network 24, which may include one or more wireless and/or wirelined communication systems; one or more non-public intranet systemsand/or public internet systems; and/or one or more local area networks(LAN) and/or wide area networks (WAN).

The DSN memory 22 includes a plurality of storage units 36 that may belocated at geographically different sites (e.g., one in Chicago, one inMilwaukee, etc.), at a common site, or a combination thereof. Forexample, if the DSN memory 22 includes eight storage units 36, eachstorage unit is located at a different site. As another example, if theDSN memory 22 includes eight storage units 36, all eight storage unitsare located at the same site. As yet another example, if the DSN memory22 includes eight storage units 36, a first pair of storage units are ata first common site, a second pair of storage units are at a secondcommon site, a third pair of storage units are at a third common site,and a fourth pair of storage units are at a fourth common site. Notethat a DSN memory 22 may include more or less than eight storage units36. Further note that each storage unit 36 includes a computing core (asshown in FIG. 2, or components thereof) and a plurality of memorydevices for storing dispersed error encoded data.

In various embodiments, each of the storage units operates as adistributed storage and task (DST) execution unit, and is operable tostore dispersed error encoded data and/or to execute, in a distributedmanner, one or more tasks on data. The tasks may be a simple function(e.g., a mathematical function, a logic function, an identify function,a find function, a search engine function, a replace function, etc.), acomplex function (e.g., compression, human and/or computer languagetranslation, text-to-voice conversion, voice-to-text conversion, etc.),multiple simple and/or complex functions, one or more algorithms, one ormore applications, etc. Hereafter, a storage unit may be interchangeablyreferred to as a dispersed storage and task (DST) execution unit and aset of storage units may be interchangeably referred to as a set of DSTexecution units.

Each of the computing devices 12-16, the managing unit 18, and theintegrity processing unit 20 include a computing core 26, which includesnetwork interfaces 30-33. Computing devices 12-16 may each be a portablecomputing device and/or a fixed computing device. A portable computingdevice may be a social networking device, a gaming device, a cell phone,a smart phone, a digital assistant, a digital music player, a digitalvideo player, a laptop computer, a handheld computer, a tablet, a videogame controller, and/or any other portable device that includes acomputing core. A fixed computing device may be a computer (PC), acomputer server, a cable set-top box, a satellite receiver, a televisionset, a printer, a fax machine, home entertainment equipment, a videogame console, and/or any type of home or office computing equipment.Note that each managing unit 18 and the integrity processing unit 20 maybe separate computing devices, may be a common computing device, and/ormay be integrated into one or more of the computing devices 12-16 and/orinto one or more of the storage units 36. In various embodiments,computing devices 12-16 can include user devices and/or can be utilizedby a requesting entity generating access requests, which can includerequests to read or write data to storage units in the DSN.

Each interface 30, 32, and 33 includes software and hardware to supportone or more communication links via the network 24 indirectly and/ordirectly. For example, interface 30 supports a communication link (e.g.,wired, wireless, direct, via a LAN, via the network 24, etc.) betweencomputing devices 14 and 16. As another example, interface 32 supportscommunication links (e.g., a wired connection, a wireless connection, aLAN connection, and/or any other type of connection to/from the network24) between computing devices 12 & 16 and the DSN memory 22. As yetanother example, interface 33 supports a communication link for each ofthe managing unit 18 and the integrity processing unit 20 to the network24.

Computing devices 12 and 16 include a dispersed storage (DS) clientmodule 34, which enables the computing device to dispersed storage errorencode and decode data as subsequently described with reference to oneor more of FIGS. 3-8. In this example embodiment, computing device 16functions as a dispersed storage processing agent for computing device14. In this role, computing device 16 dispersed storage error encodesand decodes data on behalf of computing device 14. With the use ofdispersed storage error encoding and decoding, the DSN 10 is tolerant ofa significant number of storage unit failures (the number of failures isbased on parameters of the dispersed storage error encoding function)without loss of data and without the need for a redundant or backupcopies of the data. Further, the DSN 10 stores data for an indefiniteperiod of time without data loss and in a secure manner (e.g., thesystem is very resistant to unauthorized attempts at accessing thedata).

In operation, the managing unit 18 performs DS management services. Forexample, the managing unit 18 establishes distributed data storageparameters (e.g., vault creation, distributed storage parameters,security parameters, billing information, user profile information,etc.) for computing devices 12-14 individually or as part of a group ofuser devices. As a specific example, the managing unit 18 coordinatescreation of a vault (e.g., a virtual memory block associated with aportion of an overall namespace of the DSN) within the DSN memory 22 fora user device, a group of devices, or for public access and establishesper vault dispersed storage (DS) error encoding parameters for a vault.The managing unit 18 facilitates storage of DS error encoding parametersfor each vault by updating registry information of the DSN 10, where theregistry information may be stored in the DSN memory 22, a computingdevice 12-16, the managing unit 18, and/or the integrity processing unit20.

The DSN managing unit 18 creates and stores user profile information(e.g., an access control list (ACL)) in local memory and/or withinmemory of the DSN memory 22. The user profile information includesauthentication information, permissions, and/or the security parameters.The security parameters may include encryption/decryption scheme, one ormore encryption keys, key generation scheme, and/or dataencoding/decoding scheme.

The DSN managing unit 18 creates billing information for a particularuser, a user group, a vault access, public vault access, etc. Forinstance, the DSN managing unit 18 tracks the number of times a useraccesses a non-public vault and/or public vaults, which can be used togenerate a per-access billing information. In another instance, the DSNmanaging unit 18 tracks the amount of data stored and/or retrieved by auser device and/or a user group, which can be used to generate aper-data-amount billing information.

As another example, the managing unit 18 performs network operations,network administration, and/or network maintenance. Network operationsincludes authenticating user data allocation requests (e.g., read and/orwrite requests), managing creation of vaults, establishingauthentication credentials for user devices, adding/deleting components(e.g., user devices, storage units, and/or computing devices with a DSclient module 34) to/from the DSN 10, and/or establishing authenticationcredentials for the storage units 36. Network administration includesmonitoring devices and/or units for failures, maintaining vaultinformation, determining device and/or unit activation status,determining device and/or unit loading, and/or determining any othersystem level operation that affects the performance level of the DSN 10.Network maintenance includes facilitating replacing, upgrading,repairing, and/or expanding a device and/or unit of the DSN 10.

The integrity processing unit 20 performs rebuilding of ‘bad’ or missingencoded data slices. At a high level, the integrity processing unit 20performs rebuilding by periodically attempting to retrieve/list encodeddata slices, and/or slice names of the encoded data slices, from the DSNmemory 22. For retrieved encoded slices, they are checked for errors dueto data corruption, outdated version, etc. If a slice includes an error,it is flagged as a ‘bad’ slice. For encoded data slices that were notreceived and/or not listed, they are flagged as missing slices. Badand/or missing slices are subsequently rebuilt using other retrievedencoded data slices that are deemed to be good slices to produce rebuiltslices. The rebuilt slices are stored in the DSN memory 22.

FIG. 2 is a schematic block diagram of an embodiment of a computing core26 that includes a processing module 50, a memory controller 52, mainmemory 54, a video graphics processing unit 55, an input/output (IO)controller 56, a peripheral component interconnect (PCI) interface 58,an IO interface module 60, at least one IO device interface module 62, aread only memory (ROM) basic input output system (BIOS) 64, and one ormore memory interface modules. The one or more memory interfacemodule(s) includes one or more of a universal serial bus (USB) interfacemodule 66, a host bus adapter (HBA) interface module 68, a networkinterface module 70, a flash interface module 72, a hard drive interfacemodule 74, and a DSN interface module 76.

The DSN interface module 76 functions to mimic a conventional operatingsystem (OS) file system interface (e.g., network file system (NFS),flash file system (FFS), disk file system (DFS), file transfer protocol(FTP), web-based distributed authoring and versioning (WebDAV), etc.)and/or a block memory interface (e.g., small computer system interface(SCSI), internet small computer system interface (iSCSI), etc.). The DSNinterface module 76 and/or the network interface module 70 may functionas one or more of the interface 30-33 of FIG. 1. Note that the IO deviceinterface module 62 and/or the memory interface modules 66-76 may becollectively or individually referred to as IO ports.

FIG. 3 is a schematic block diagram of an example of dispersed storageerror encoding of data. When a computing device 12 or 16 has data tostore it disperse storage error encodes the data in accordance with adispersed storage error encoding process based on dispersed storageerror encoding parameters. Here, the computing device stores data object40, which can include a file (e.g., text, video, audio, etc.), or otherdata arrangement. The dispersed storage error encoding parametersinclude an encoding function (e.g., information dispersal algorithm(IDA), Reed-Solomon, Cauchy Reed-Solomon, systematic encoding,non-systematic encoding, on-line codes, etc.), a data segmentingprotocol (e.g., data segment size, fixed, variable, etc.), and per datasegment encoding values. The per data segment encoding values include atotal, or pillar width, number (T) of encoded data slices per encodingof a data segment i.e., in a set of encoded data slices); a decodethreshold number (D) of encoded data slices of a set of encoded dataslices that are needed to recover the data segment; a read thresholdnumber (R) of encoded data slices to indicate a number of encoded dataslices per set to be read from storage for decoding of the data segment;and/or a write threshold number (W) to indicate a number of encoded dataslices per set that must be accurately stored before the encoded datasegment is deemed to have been properly stored. The dispersed storageerror encoding parameters may further include slicing information (e.g.,the number of encoded data slices that will be created for each datasegment) and/or slice security information (e.g., per encoded data sliceencryption, compression, integrity checksum, etc.).

In the present example, Cauchy Reed-Solomon has been selected as theencoding function (a generic example is shown in FIG. 4 and a specificexample is shown in FIG. 5); the data segmenting protocol is to dividethe data object into fixed sized data segments; and the per data segmentencoding values include: a pillar width of 5, a decode threshold of 3, aread threshold of 4, and a write threshold of 4. In accordance with thedata segmenting protocol, the computing device 12 or 16 divides dataobject 40 into a plurality of fixed sized data segments (e.g., 1 throughY of a fixed size in range of Kilo-bytes to Tera-bytes or more). Thenumber of data segments created is dependent of the size of the data andthe data segmenting protocol.

The computing device 12 or 16 then disperse storage error encodes a datasegment using the selected encoding function (e.g., Cauchy Reed-Solomon)to produce a set of encoded data slices. FIG. 4 illustrates a genericCauchy Reed-Solomon encoding function, which includes an encoding matrix(EM), a data matrix (DM), and a coded matrix (CM). The size of theencoding matrix (EM) is dependent on the pillar width number (T) and thedecode threshold number (D) of selected per data segment encodingvalues. To produce the data matrix (DM), the data segment is dividedinto a plurality of data blocks and the data blocks are arranged into Dnumber of rows with Z data blocks per row. Note that Z is a function ofthe number of data blocks created from the data segment and the decodethreshold number (D). The coded matrix is produced by matrix multiplyingthe data matrix by the encoding matrix.

FIG. 5 illustrates a specific example of Cauchy Reed-Solomon encodingwith a pillar number (T) of five and decode threshold number of three.In this example, a first data segment is divided into twelve data blocks(D1-D12). The coded matrix includes five rows of coded data blocks,where the first row of X11-X14 corresponds to a first encoded data slice(EDS 1_1), the second row of X21-X24 corresponds to a second encodeddata slice (EDS 2_1), the third row of X31-X34 corresponds to a thirdencoded data slice (EDS 3_1), the fourth row of X41-X44 corresponds to afourth encoded data slice (EDS 4_1), and the fifth row of X51-X54corresponds to a fifth encoded data slice (EDS 5_1). Note that thesecond number of the EDS designation corresponds to the data segmentnumber.

Returning to the discussion of FIG. 3, the computing device also createsa slice name (SN) for each encoded data slice (EDS) in the set ofencoded data slices. A typical format for a slice name 80 is shown inFIG. 6. As shown, the slice name (SN) 80 includes a pillar number of theencoded data slice (e.g., one of 1-T), a data segment number (e.g., oneof 1-Y), a vault identifier (ID), a data object identifier (ID), and mayfurther include revision level information of the encoded data slices.The slice name functions as, at least part of, a DSN address for theencoded data slice for storage and retrieval from the DSN memory 22.

As a result of encoding, the computing device 12 or 16 produces aplurality of sets of encoded data slices, which are provided with theirrespective slice names to the storage units for storage. As shown, thefirst set of encoded data slices includes EDS 1_1 through EDS 5_1 andthe first set of slice names includes SN 1_1 through SN 5_1 and the lastset of encoded data slices includes EDS 1_Y through EDS 5_Y and the lastset of slice names includes SN 1_Y through SN 5_Y.

FIG. 7 is a schematic block diagram of an example of dispersed storageerror decoding of a data object that was dispersed storage error encodedand stored in the example of FIG. 4. In this example, the computingdevice 12 or 16 retrieves from the storage units at least the decodethreshold number of encoded data slices per data segment. As a specificexample, the computing device retrieves a read threshold number ofencoded data slices.

To recover a data segment from a decode threshold number of encoded dataslices, the computing device uses a decoding function as shown in FIG.8. As shown, the decoding function is essentially an inverse of theencoding function of FIG. 4. The coded matrix includes a decodethreshold number of rows (e.g., three in this example) and the decodingmatrix in an inversion of the encoding matrix that includes thecorresponding rows of the coded matrix. For example, if the coded matrixincludes rows 1, 2, and 4, the encoding matrix is reduced to rows 1, 2,and 4, and then inverted to produce the decoding matrix.

FIG. 9 is a schematic block diagram of another embodiment of a dispersedstorage network (DSN) that includes a computing device 16 of FIG. 1, thenetwork 24 of FIG. 1, and at least one storage unit 910. The storageunit 910 can include the interface 32 of FIG. 1 and the computing core26 of FIG. 1, and can be implemented by utilizing the storage unit 36 ofFIG. 1. The storage unit 910 can include one or more memory devices 920,and each memory device 920 can be divided into a plurality of storagezones, including storage zones 922-1 and 922-2. Each storage zone caninclude a subset of data objects, data segments, and/or data slicesstored by the memory device 920, which can include data slices 930-1,930-2, 930-3, and 930-4. The storage unit can also include a RAM 945,which can include a volatile memory or other memory, and which can beimplemented by utilizing computing core 26. The RAM 945 can include aplurality of append points, including append point 956-1 and appendpoint 956-2, where the plurality of append points correspond to memorylocations of the plurality of storage zones where the next data shouldbe stored according to a sequential or append only write protocol. TheRAM 945 can also include a plurality of pointers corresponding to dataslices stored in the storage unit that include memory locations, offsetinformation, zone information, and/or memory device information suchthat the corresponding data slice can be fetched from memory byutilizing its corresponding pointer. The DSN functions to store datasequentially in zones.

A major component of request latency on a DSN is the time storage unitsspend reading data from and writing data to memory devices. Generally, alarge portion of the time a memory device spends reading or writing datais seeking to the track and sector where the requested data is located.One way to fully control memory device seeking is to bypass formattingmemory devices of storage units with a filesystem and instead read andwrite directly on the raw memory device over supported protocols, forexample, by utilizing the Small Computer System Interface (SCSI)protocol or other protocol that supports writing directly to raw memory.To support sequential writes and/or data removal, one or more memorydevices 920 of a storage unit can be split into fixed-sized zones, wherethe storage unit utilizes a fully sequential write protocol. Forexample, a storage unit can be implemented by utilizing Append OptimalStorage Devices (AOSD) or other memory devices for which appended writesare the optimal form of access, and/or for which an append-only writescheme is utilized when storing data. The append-only write schemedictates that new data objects and/or slices are written by beingappended to an end, or “append point” of a zone in storage, such asstorage zone 922-1 and 922-2. As data slices are written, they arewritten to the next space in their respective zone of memory accordingto the corresponding append point of the zone, and the append point isupdated based on the length of newly written data, such as data slices930-1-930-4. Append points for each zone, such as append points 956-1and 956-2, can be maintained in a volatile memory such as RAM 945 orother memory of the storage unit, and can be stored as a pointer orother reference to the append point location of the memory device.

The storage unit can dynamically allocate new zones and un-allocate oldzones of one or more memory devices to maintain a fixed number of activezones and/or a number of active zones that is determined to be optimal.The number of zones and/or the zones selected in the subset can bedetermined based on zone allocation parameters and/or zone reallocationparameters, which can be based on I/O request frequency, memory and/orprocessing requirements, I/O speed requirements, and/or other zoneallocation and/or reallocation requirements. Selecting a smaller subsetof zones open for write can further minimize seeking and thus improveI/O speed. In some embodiments, exactly one zone per memory device isopen for writing at any given time. This can eliminates seeking on eachmemory device as writing is fully sequential on each memory device. Invarious embodiments, the active zone can be selected based on availablespace in the zone, based on a previously selected zone, and/or selectedrandomly. The storage unit can maintain information regarding whichzones are designated as open to writes and/or reads, and which zones areclosed to writes and/or reads, and can change these designations inresponse to determining a reallocation requirement is met. The storageunit can also maintain zone priority information and/or availablecapacity information for each of the zones. This information can bestored in RAM 945 or other memory of the storage unit.

In a purely write-based workload on a DSN, the aforementionedenhancements can reduce memory device seeking to a single time when anew zone is allocated and no further seeking will be required until anew zone needs to be allocated. There are also enhancements that can beemployed with regard to reading data from memory devices. This caninclude maintaining pointers, such as pointers 940-1-940-3, for all datathat describe exactly where on the memory device any requested data isstored, thereby reducing to a single seek for reading the data. Suchpointers can be stored on a faster memory, such as a RAM 945 or othermemory of the storage device. The pointers can include information aboutthe memory device, zone, file, offset, and/or length of the data slice.

Another strategy used by storage units to facilitate faster readsincludes caching reads intelligently in faster volatile memory such asRAM 945, for example on a frequency-based policy where data that is usedfrequently stays in the volatile memory. The read frequency of a dataslice can be received from a computing device 16 or other entity via thenetwork, for example as a priority indicator when the data is firstwritten or later based on a change in data priority. The storage unitcan also track read frequency of data slices, and can determine to movea data slice to the volatile memory when the read frequency, forexample, a number of reads in a fixed time period, exceeds or otherwisecompares favorably to a predefined read frequency threshold.

Another strategy used by storage units to minimize the time spentseeking during I/O includes caching incoming reads and/or writes infaster volatile memory, such as RAM 945, and/or writing larger amountsof data sequentially in batches to the persistent memory device and/orzone. Flushing data from the cache may be done on a periodic basis, forexample every one second, at another fixed time interval, in response toreceiving a flush requirement, and/or if the usage of the volatilememory is approaching, exceeds, or otherwise compares unfavorably to apredefined threshold. Flushing the data can include generating a largedata object that includes the plurality of data slices, where the dataslices are organized within the large data object based on a protocolthat may or may not be sequential. The large data object is writtensequentially to the persistent memory device and/or zone.

Caching incoming reads and/or writes can also be used to minimize thenumber and frequencies of switching between zones. While writing to onezone in a memory device, writes of new data destined for one or moreother zones can be queued in one or more corresponding caches, forexample, stored in RAM 945. The storage unit can queue data based ontime received or other data priority requirements. The storage unit candetermine which zone data is queued for based on data dependency, thesize of the data, the available space in the other zones, namespaceand/or mapping requirements, or other location requirements that dictateif certain data must be stored in a certain zone. In variousembodiments, some or all data is queued up randomly. A storage unit candetermines it is optimal to switch zones and/or select the new zone inresponse to cache capacity approaching, exceeding, or otherwisecomparing unfavorably to a predefined cache capacity threshold. Astorage unit can switch to a new zone based on data timing and/or datadependency requirements, for example, by determining a journal entrymust be written prior to some content entry, determining that a largeamount of high priority data is stored in a queue, and/or determiningthat a data slice in a queue must be written by a certain deadline. Oncethe switch is performed, the storage unit can write the new data in thecache, and flush the cache of a queue destined for the new zone.

In various embodiments, a processing system a storage unit of a DSNincludes at least one processor and a memory that stores operationalinstructions, that when executed by the at least one processor cause theprocessing system to select a first one of a plurality of storage zonesof a memory device of the storage unit based on zone allocationparameters. The first one of the plurality of storage zones isdesignated as open for writes. A first data slice is received via anetwork for storage. The first data slice is written sequentially at amemory location of the first one of the plurality of storage zones basedon determining that the first one of the plurality of storage zones isdesignated as open for writes. A pointer corresponding to the first dataslice that indicates the first one of the plurality of storage zones andthe memory location is generated. A first read request is received viathe network from a requesting entity that indicates the first dataslice. The first data slice is retrieved from the memory device based onthe pointer, and is transmitted to the requesting entity.

FIG. 10 is a flowchart illustrating an example of storing datasequentially in zones. In particular, a method is presented for use inassociation with one or more functions and features described inconjunction with FIGS. 1-9, for execution by a storage unit includes aprocessor or via another processing system of a dispersed storagenetwork that includes at least one processor and memory that storesinstruction that configure the processor or processors to perform thesteps described below. Step 1002 includes selecting a first one of aplurality of storage zones of a memory device of the storage unit basedon zone allocation parameters. Step 1004 includes designating the firstone of the plurality of storage zones as open for writes. Step 1006includes receiving, via a network, a first data slice for storage. Step1008 includes writing the first data slice sequentially at a memorylocation of the first one of the plurality of storage zones based ondetermining that the first one of the plurality of storage zones isdesignated as open for writes. Step 1010 includes generating a pointercorresponding to the first data slice that indicates the first one ofthe plurality of storage zones and the memory location. Step 1012includes receiving, via the network, a first read request from arequesting entity that indicates the first data slice. Step 1014includes retrieving the first data slice from the memory device based onthe pointer. Step 1016 includes transmitting the first data slice to therequesting entity.

In various embodiments, the first data slice is written sequentiallybased on a small computer system interface protocol. In variousembodiments, the first data slice is written sequentially based on anappend point, and the append point is updated after the first data sliceis written based on a length of the first data slice.

In various embodiments, a zone reallocation requirement is determined ata time after the first data slice is written. A second one of theplurality of storage zones that is designated as closed for writes isselected based on the zone reallocation requirement, and the second oneof the plurality of storage zones is then designated as open for writes.A second data slice is received via the network for storage. The seconddata slice is written sequentially at a memory location of the secondone of the plurality of storage zones based on determining that thesecond one of the plurality of storage zones is designated as open forwrites.

In various embodiments, exactly one storage zone is selected anddesignated as open for writes based on the zone allocation parameters,where the exactly one storage zone is the first one of the plurality ofstorage zones. All remaining storage zones of the plurality of storagezones that are not the exactly one storage zone are designated as closedfor writes. In various embodiments, a subset of storage zones isselected from the plurality of storage zones based on the zoneallocation parameters. A size of the subset of storage zones is selectedbased on the zone allocation parameters, and the subset of storage zonesincludes the first one of the plurality of storage zones. The subset ofstorage zones is designated as open for writes. All storage zones in theplurality of storage zones that are not included in the subset ofstorage zones are designated as closed for writes.

In various embodiments, a subset of data slices from a plurality of dataslices stored on the memory device that compare favorably to a readfrequency threshold is identified. The subset of data slices is storedin a volatile memory of the storage unit, where reading the subset ofdata slices from the volatile memory is faster than reading the subsetof data slices from the memory device. a second read request thatindicates a second data slice is received via the network. The storageunit determines that the second data slice is stored in the volatilememory, and retrieves the second data slice from the volatile memory fortransmission to the requesting entity via the network.

In various embodiments, a plurality of data slice write requests arereceived via the network, where the plurality of data slice writerequests include a plurality of data slices. The plurality of dataslices in a cache of the storage unit. The cache is flushed in responseto a determining a cache flush requirement by generating a data objectthat includes the plurality of data slices, by writing the data objectsequentially to the to the first one of the plurality of storage zonesin response to determining the first one of the plurality of storagezones is designated as open for writes, and by removing the plurality ofdata slices from the cache.

In various embodiments, a subset of the plurality of storage zones thatdoes not include the first one of the plurality of storage zones aredesignated as closed for writes. A plurality of data slice writerequests are received via the network, where the plurality of data slicewrite requests includes a plurality of data slices. The plurality ofdata slices are stored in a cache of the storage unit, where storing thedata slices includes assigning each of the plurality of data slices toone of a plurality of queues in the cache, and where each one of theplurality of queues corresponds to a storage zone in the subset of theplurality of storage zones designated as closed for writing. A zonereallocation requirement is determined after the plurality of dataslices are stored in the cache. A second one of the plurality of storagezones is selected based on the zone reallocation requirement, the secondone of the plurality of storage zones is included in the subset. Thesecond one of the plurality of storage zones is designated as open forwrites. A first one of the plurality of queues that corresponds to thesecond one of the plurality of storage zones is flushed from the cache,where the flushing includes writing the plurality of data slices in thefirst one of the plurality of queues sequentially to the second one ofthe plurality of storage zones in response to determining the second oneof the plurality of storage zones is designated as open for writes andfurther includes deleting the first one of the plurality of queues fromthe cache.

In various embodiments, the zone reallocation requirement is based on acapacity of the cache comparing unfavorably to a cache capacityrequirement. In various embodiments, the second one of the plurality ofstorage zones is selected based on a queue priority rankingcorresponding to the plurality of queues, and the second one of theplurality of storage zones corresponds to a highest priority ranking ofthe queue priority ranking. In various embodiments, the queue priorityranking is based on a data dependency requirement, and the second one ofthe plurality of storage zones is assigned the highest priority rankingin response to determining that a second data slice in the second one ofthe plurality of storage zones must be written before a third data slicein a third one of the plurality of storage zones according to the datadependency requirement.

In various embodiments, a non-transitory computer readable storagemedium includes at least one memory section that stores operationalinstructions that, when executed by a processing system of a dispersedstorage network (DSN) that includes a processor and a memory, causes theprocessing system to select a first one of a plurality of storage zonesof a memory device based on zone allocation parameters. The first one ofthe plurality of storage zones is designated as open for writes. A firstdata slice is received via a network for storage. The first data sliceis written sequentially at a memory location of the first one of theplurality of storage zones based on determining that the first one ofthe plurality of storage zones is designated as open for writes. Apointer corresponding to the first data slice that indicates the firstone of the plurality of storage zones and the memory location isgenerated. A first read request is received via the network from arequesting entity that indicates the first data slice. The first dataslice is retrieved from the memory device based on the pointer, and istransmitted to the requesting entity.

It is noted that terminologies as may be used herein such as bit stream,stream, signal sequence, etc. (or their equivalents) have been usedinterchangeably to describe digital information whose contentcorresponds to any of a number of desired types (e.g., data, video,speech, audio, etc. any of which may generally be referred to as‘data’).

As may be used herein, the terms “substantially” and “approximately”provides an industry-accepted tolerance for its corresponding termand/or relativity between items. Such an industry-accepted toleranceranges from less than one percent to fifty percent and corresponds to,but is not limited to, component values, integrated circuit processvariations, temperature variations, rise and fall times, and/or thermalnoise. Such relativity between items ranges from a difference of a fewpercent to magnitude differences. As may also be used herein, theterm(s) “configured to”, “operably coupled to”, “coupled to”, and/or“coupling” includes direct coupling between items and/or indirectcoupling between items via an intervening item (e.g., an item includes,but is not limited to, a component, an element, a circuit, and/or amodule) where, for an example of indirect coupling, the intervening itemdoes not modify the information of a signal but may adjust its currentlevel, voltage level, and/or power level. As may further be used herein,inferred coupling (i.e., where one element is coupled to another elementby inference) includes direct and indirect coupling between two items inthe same manner as “coupled to”. As may even further be used herein, theterm “configured to”, “operable to”, “coupled to”, or “operably coupledto” indicates that an item includes one or more of power connections,input(s), output(s), etc., to perform, when activated, one or more itscorresponding functions and may further include inferred coupling to oneor more other items. As may still further be used herein, the term“associated with”, includes direct and/or indirect coupling of separateitems and/or one item being embedded within another item.

As may be used herein, the term “compares favorably”, indicates that acomparison between two or more items, signals, etc., provides a desiredrelationship. For example, when the desired relationship is that signal1 has a greater magnitude than signal 2, a favorable comparison may beachieved when the magnitude of signal 1 is greater than that of signal 2or when the magnitude of signal 2 is less than that of signal 1. As maybe used herein, the term “compares unfavorably”, indicates that acomparison between two or more items, signals, etc., fails to providethe desired relationship.

As may also be used herein, the terms “processing module”, “processingcircuit”, “processor”, and/or “processing unit” may be a singleprocessing device or a plurality of processing devices. Such aprocessing device may be a microprocessor, micro-controller, digitalsignal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, analog circuitry, digital circuitry, and/or any device thatmanipulates signals (analog and/or digital) based on hard coding of thecircuitry and/or operational instructions. The processing module,module, processing circuit, and/or processing unit may be, or furtherinclude, memory and/or an integrated memory element, which may be asingle memory device, a plurality of memory devices, and/or embeddedcircuitry of another processing module, module, processing circuit,and/or processing unit. Such a memory device may be a read-only memory,random access memory, volatile memory, non-volatile memory, staticmemory, dynamic memory, flash memory, cache memory, and/or any devicethat stores digital information. Note that if the processing module,module, processing circuit, and/or processing unit includes more thanone processing device, the processing devices may be centrally located(e.g., directly coupled together via a wired and/or wireless busstructure) or may be distributedly located (e.g., cloud computing viaindirect coupling via a local area network and/or a wide area network).Further note that if the processing module, module, processing circuit,and/or processing unit implements one or more of its functions via astate machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory and/or memory element storing the correspondingoperational instructions may be embedded within, or external to, thecircuitry comprising the state machine, analog circuitry, digitalcircuitry, and/or logic circuitry. Still further note that, the memoryelement may store, and the processing module, module, processingcircuit, and/or processing unit executes, hard coded and/or operationalinstructions corresponding to at least some of the steps and/orfunctions illustrated in one or more of the Figures. Such a memorydevice or memory element can be included in an article of manufacture.

One or more embodiments have been described above with the aid of methodsteps illustrating the performance of specified functions andrelationships thereof. The boundaries and sequence of these functionalbuilding blocks and method steps have been arbitrarily defined hereinfor convenience of description. Alternate boundaries and sequences canbe defined so long as the specified functions and relationships areappropriately performed. Any such alternate boundaries or sequences arethus within the scope and spirit of the claims. Further, the boundariesof these functional building blocks have been arbitrarily defined forconvenience of description. Alternate boundaries could be defined aslong as the certain significant functions are appropriately performed.Similarly, flow diagram blocks may also have been arbitrarily definedherein to illustrate certain significant functionality.

To the extent used, the flow diagram block boundaries and sequence couldhave been defined otherwise and still perform the certain significantfunctionality. Such alternate definitions of both functional buildingblocks and flow diagram blocks and sequences are thus within the scopeand spirit of the claims. One of average skill in the art will alsorecognize that the functional building blocks, and other illustrativeblocks, modules and components herein, can be implemented as illustratedor by discrete components, application specific integrated circuits,processors executing appropriate software and the like or anycombination thereof.

In addition, a flow diagram may include a “start” and/or “continue”indication. The “start” and “continue” indications reflect that thesteps presented can optionally be incorporated in or otherwise used inconjunction with other routines. In this context, “start” indicates thebeginning of the first step presented and may be preceded by otheractivities not specifically shown. Further, the “continue” indicationreflects that the steps presented may be performed multiple times and/ormay be succeeded by other activities not specifically shown. Further,while a flow diagram indicates a particular ordering of steps, otherorderings are likewise possible provided that the principles ofcausality are maintained.

The one or more embodiments are used herein to illustrate one or moreaspects, one or more features, one or more concepts, and/or one or moreexamples. A physical embodiment of an apparatus, an article ofmanufacture, a machine, and/or of a process may include one or more ofthe aspects, features, concepts, examples, etc. described with referenceto one or more of the embodiments discussed herein. Further, from figureto figure, the embodiments may incorporate the same or similarly namedfunctions, steps, modules, etc. that may use the same or differentreference numbers and, as such, the functions, steps, modules, etc. maybe the same or similar functions, steps, modules, etc. or differentones.

Unless specifically stated to the contra, signals to, from, and/orbetween elements in a figure of any of the figures presented herein maybe analog or digital, continuous time or discrete time, and single-endedor differential. For instance, if a signal path is shown as asingle-ended path, it also represents a differential signal path.Similarly, if a signal path is shown as a differential path, it alsorepresents a single-ended signal path. While one or more particulararchitectures are described herein, other architectures can likewise beimplemented that use one or more data buses not expressly shown, directconnectivity between elements, and/or indirect coupling between otherelements as recognized by one of average skill in the art.

The term “module” is used in the description of one or more of theembodiments. A module implements one or more functions via a device suchas a processor or other processing device or other hardware that mayinclude or operate in association with a memory that stores operationalinstructions. A module may operate independently and/or in conjunctionwith software and/or firmware. As also used herein, a module may containone or more sub-modules, each of which may be one or more modules.

As may further be used herein, a computer readable memory includes oneor more memory elements. A memory element may be a separate memorydevice, multiple memory devices, or a set of memory locations within amemory device. Such a memory device may be a read-only memory, randomaccess memory, volatile memory, non-volatile memory, static memory,dynamic memory, flash memory, cache memory, and/or any device thatstores digital information. The memory device may be in a form a solidstate memory, a hard drive memory, cloud memory, thumb drive, servermemory, computing device memory, and/or other physical medium forstoring digital information.

While particular combinations of various functions and features of theone or more embodiments have been expressly described herein, othercombinations of these features and functions are likewise possible. Thepresent disclosure is not limited by the particular examples disclosedherein and expressly incorporates these other combinations.

What is claimed is:
 1. A method for execution by a storage unit of adispersed storage network (DSN) that includes a processor, the methodcomprises: determining zone allocation parameters; selecting a first oneof a plurality of storage zones of a memory device of the storage unitto be open for writes based on the zone allocation parameters; selectinga second one of the plurality of storage zones of a memory device of thestorage unit to be closed for writes based on the zone allocationparameters indicating a requirement for exactly a fixed number ofstorage zones to be designated as open for writes; designating the firstone of the plurality of storage zones as open for writes in response toselecting the first one of a plurality of storage zones to be open forwrites; designating the second one of the plurality of storage zones asclosed for writes in response to selecting the second one of theplurality of storage zones to be closed for writes; receiving, via anetwork, a first data slice for storage after designating the first oneof the plurality of storage zones as open for writes; writing the firstdata slice sequentially at a memory location of the first one of theplurality of storage zones based on determining that the first one ofthe plurality of storage zones is designated as open for writes;generating a pointer corresponding to the first data slice thatindicates the first one of the plurality of storage zones and the memorylocation; receiving, via the network, a first read request from arequesting entity that indicates the first data slice; retrieving thefirst data slice from the memory device based on the pointer;transmitting the first data slice to the requesting entity; determininga zone reallocation requirement at a time after the first data slice iswritten; selecting the second one of the plurality of storage zones tobecome open for writes based on the zone reallocation requirement; anddesignating the second one of the plurality of storage zones as open forwrites in response to selecting the second one of the plurality ofstorage zones based on the zone reallocation requirement.
 2. The methodof claim 1, wherein the first data slice is written sequentially basedon a small computer system interface protocol.
 3. The method of claim 1,wherein the first data slice is written sequentially based on an appendpoint, and wherein the append point is updated after the first dataslice is written based on a length of the first data slice.
 4. Themethod of claim 1, wherein exactly one storage zone is selected anddesignated as open for writes based on the zone allocation parameters,wherein the exactly one storage zone is the first one of the pluralityof storage zones, and wherein the method further comprises: designatingall remaining storage zones of the plurality of storage zones that arenot the exactly one storage zone as closed for writes.
 5. The method ofclaim 1, further comprising: selecting a first subset of storage zonesto be open for writes from the plurality of storage zones based on thezone allocation parameters, wherein a number of storage zones of thefirst subset of storage zones is selected to be the fixed number ofstorage zones to be designated as open for writes indicated in the zoneallocation parameters, and wherein the first subset of storage zonesincludes the first one of the plurality of storage zones and does notinclude the second one of the plurality of storage zones; designatingthe first subset of storage zones as open for writes; designating allstorage zones in the plurality of storage zones that are not included inthe first subset of storage zones as closed for writes; selecting asecond subset of storage zones to be open for writes from the pluralityof storage zones based on the zone reallocation requirement, wherein thesecond subset of storage zones includes the second one of the pluralityof storage zones, wherein the zone reallocation requirement includes arequirement to maintain the fixed number of storage zones as open forwrites, wherein the number of storage zones is included in the secondsubset of storage zones in response to the requirement to maintain thefixed number of storage zones as open for writes; and selecting thefirst one of the plurality of storage zones to be closed for writesbased on selecting the second one of the plurality of storage zones tobe open for writes to meet the requirement to maintain the a fixednumber of storage zones as open for writes.
 6. The method of claim 1,further comprising: receiving, via a network, a second data slice forstorage; and writing the second data slice sequentially at a memorylocation of the second one of the plurality of storage zones based ondetermining that the second one of the plurality of storage zones isdesignated as open for writes.
 7. The method of claim 1, furthercomprising: tracking read frequency of a plurality of data slices storedon the memory device; identifying a subset of data slices from theplurality of data slices stored on the memory device with tracked readfrequencies that compare favorably to a read frequency threshold;transferring storage of the subset of data slices from the memory deviceto a volatile memory of the storage unit, wherein reading the subset ofdata slices from the volatile memory is faster than reading the subsetof data slices from the memory device; receiving, via the network, asecond read request that indicates a second data slice; determining thatthe second data slice is stored in the volatile memory; and retrievingthe second data slice from the volatile memory for transmission to therequesting entity via the network.
 8. The method of claim 1, furthercomprising: receiving, via the network, a plurality of data slice writerequests, wherein the plurality of data slice write requests includes aplurality of data slices; storing the plurality of data slices in acache of the storage unit; and flushing the cache in response to adetermining a cache flush requirement by generating a data object thatincludes the plurality of data slices, by writing the data objectsequentially to the to the first one of the plurality of storage zonesin response to determining the first one of the plurality of storagezones is designated as open for writes, and by removing the plurality ofdata slices from the cache.
 9. The method of claim 1, furthercomprising: designating a subset of the plurality of storage zones thatdoes not include the first one of the plurality of storage zones asclosed for writes, wherein the subset of the plurality of storage zonesincludes the second one of the plurality of storage zones; receiving,via the network, a plurality of data slice write requests, wherein theplurality of data slice write requests includes a plurality of dataslices; storing the plurality of data slices in a cache of the storageunit by assigning each of the plurality of data slices to one of aplurality of queues in the cache, wherein each one of the plurality ofqueues corresponds to a storage zone in the subset of the plurality ofstorage zones designated as closed for writes, and wherein each of theplurality of queues includes ones of the plurality of data slicesdesignated for storage in the corresponding storage zone; determiningthe zone reallocation requirement after the plurality of data slices arestored in the cache; and flushing a first one of the plurality of queuesthat corresponds to the second one of the plurality of storage zonesfrom the cache by writing the plurality of data slices in the first oneof the plurality of queues sequentially to the second one of theplurality of storage zones in response to determining the second one ofthe plurality of storage zones is designated as open for writes, and bydeleting the first one of the plurality of queues from the cache. 10.The method of claim 9, wherein the zone reallocation requirement isbased on a capacity of the cache comparing unfavorably to a cachecapacity requirement.
 11. The method of claim 9, wherein the second oneof the plurality of storage zones is selected based on a queue priorityranking corresponding to the plurality of queues, and wherein the secondone of the plurality of storage zones corresponds to a highest priorityranking of the queue priority ranking.
 12. The method of claim 11,wherein the queue priority ranking is based on a data dependencyrequirement, and wherein the second one of the plurality of storagezones is assigned the highest priority ranking in response todetermining that a second data slice in the second one of the pluralityof storage zones must be written before a third data slice in a thirdone of the plurality of storage zones according to the data dependencyrequirement.
 13. A processing system of a storage unit in a dispersedstorage network (DSN) comprises: at least one processor; a memory thatstores operational instructions, that when executed by the at least oneprocessor cause the processing system to: determine zone allocationparameters; select a first one of a plurality of storage zones of amemory device of the storage unit to be open for writes based on thezone allocation parameters; select a second one of the plurality ofstorage zones of a memory device of the storage unit to be closed forwrites based on the zone allocation parameters indicating a requirementfor exactly a fixed number of storage zones to be designated as open forwrites; designate the first one of the plurality of storage zones asopen for writes in response to selecting the first one of a plurality ofstorage zones to be open for writes; designate the second one of theplurality of storage zones as closed for writes in response to selectingthe second one of the plurality of storage zones to be closed for writesreceive, via a network, a first data slice for storage after designatingthe first one of the plurality of storage zones as open for writes;write the first data slice sequentially at a memory location of thefirst one of the plurality of storage zones based on determining thatthe first one of the plurality of storage zones is designated as openfor writes; generate a pointer corresponding to the first data slicethat indicates the first one of the plurality of storage zones and thememory location; receive, via the network, a first read request from arequesting entity that indicates the first data slice; retrieve thefirst data slice from the memory device based on the pointer; transmitthe first data slice to the requesting entity; determining a zonereallocation requirement at a time after the first data slice iswritten; selecting the second one of the plurality of storage zones tobecome open for writes based on the zone reallocation requirement; anddesignating the second one of the plurality of storage zones as open forwrites in response to selecting the second one of the plurality ofstorage zones based on the zone reallocation requirement.
 14. Theprocessing system of claim 13, wherein the first data slice is writtensequentially based on a small computer system interface protocol. 15.The processing system of claim 13, wherein the first data slice iswritten sequentially based on an append point, and wherein the appendpoint is updated after the first data slice is written based on a lengthof the first data slice.
 16. The processing system of claim 13, whereinthe operational instructions, when executed by the at least oneprocessor, further cause the processing system to: receive, via anetwork, a second data slice for storage; and write the second dataslice sequentially at a memory location of the second one of theplurality of storage zones based on determining that the second one ofthe plurality of storage zones is designated as open for writes.
 17. Theprocessing system of claim 13, wherein the operational instructions,when executed by the at least one processor, further cause theprocessing system to: track read frequency of a plurality of data slicesstored on the memory device; identify a subset of data slices from theplurality of data slices stored on the memory device with tracked readfrequencies that compare favorably to a read frequency threshold;transfer storage of the subset of data slices from the memory device toa volatile memory of the storage unit, wherein reading the subset ofdata slices from the volatile memory is faster than reading the subsetof data slices from the memory device; receive, via the network, asecond read request that indicates a second data slice; determine thatthe second data slice is stored in the volatile memory; and retrieve thesecond data slice from the volatile memory for transmission to therequesting entity via the network.
 18. The processing system of claim13, wherein the operational instructions, when executed by the at leastone processor, further cause the processing system to: receive, via thenetwork, a plurality of data slice write requests, wherein the pluralityof data slice write requests include a plurality of data slices; storethe plurality of data slices in a cache of the storage unit; and flushthe cache in response to a determining a cache flush requirement bygenerating a data object that includes the plurality of data slices, bywriting the data object sequentially to the to the first one of theplurality of storage zones in response to determining the first one ofthe plurality of storage zones is designated as open for writes, and byremoving the plurality of data slices from the cache.
 19. The processingsystem of claim 13, wherein the operational instructions, when executedby the at least one processor, further cause the processing system to:designate a subset of the plurality of storage zones that does notinclude the first one of the plurality of storage zones as closed forwrites, wherein the subset of the plurality of storage zones includesthe second one of the plurality of storage zones; receive, via thenetwork, a plurality of data slice write requests, wherein the pluralityof data slice write requests includes a plurality of data slices; storethe plurality of data slices in a cache of the storage unit by assigningeach of the plurality of data slices to one of a plurality of queues inthe cache, wherein each one of the plurality of queues corresponds to astorage zone in the subset of the plurality of storage zones designatedas closed for writes, and wherein each of the plurality of queuesincludes ones of the plurality of data slices designated for storage inthe corresponding storage zone; determine the zone reallocationrequirement after the plurality of data slices are stored in the cache;and flush a first one of the plurality of queues that corresponds to thesecond one of the plurality of storage zones from the cache by writingthe plurality of data slices in the first one of the plurality of queuessequentially to the second one of the plurality of storage zones inresponse to determining the second one of the plurality of storage zonesis designated as open for writes, and by deleting the first one of theplurality of queues from the cache.
 20. A non-transitory computerreadable storage medium comprises: at least one memory section thatstores operational instructions that, when executed by a processingsystem of a dispersed storage network (DSN) that includes a processorand a memory, causes the processing system to: determine zone allocationparameters; select a first one of a plurality of storage zones of amemory device to be open for writes based on the zone allocationparameters; select a second one of the plurality of storage zones of amemory device of to be closed for writes based on the zone allocationparameters indicating a requirement for exactly a fixed number ofstorage zones to be designated as open for writes; designate the firstone of the plurality of storage zones as open for writes in response toselecting the first one of a plurality of storage zones to be open forwrites; designate the second one of the plurality of storage zones asclosed for writes in response to selecting the second one of theplurality of storage zones to be closed for writes receive, via anetwork, a first data slice for storage after designating the first oneof the plurality of storage zones as open for writes; write the firstdata slice sequentially at a memory location of the first one of theplurality of storage zones based on determining that the first one ofthe plurality of storage zones is designated as open for writes;generate a pointer corresponding to the first data slice that indicatesthe first one of the plurality of storage zones and the memory location;receive, via the network, a first read request from a requesting entitythat indicates the first data slice; retrieve the first data slice fromthe memory device based on the pointer; transmit the first data slice tothe requesting entity; determine a zone reallocation requirement at atime after the first data slice is written; select the second one of theplurality of storage zones to become open for writes based on the zonereallocation requirement; and designate the second one of the pluralityof storage zones as open for writes in response to selecting the secondone of the plurality of storage zones based on the zone reallocationrequirement.
 21. A method for execution by a storage unit of a dispersedstorage network (DSN) that includes a processor, the method comprises:determining zone allocation parameters; selecting a first one of aplurality of storage zones of a memory device of the storage unit basedon zone allocation parameters; selecting a second one of the pluralityof storage zones of a memory device of the storage unit to be closed forwrites based on the zone allocation parameters indicating a requirementfor exactly a fixed number of storage zones to be designated as open forwrites; designating the first one of the plurality of storage zones asopen for writes in response to selecting the first one of a plurality ofstorage zones to be open for writes; designating the second one of theplurality of storage zones as closed for writes in response to selectingthe second one of the plurality of storage zones to be closed for writesreceiving, via a network, a first data slice for storage afterdesignating the first one of the plurality of storage zones as open forwrites; writing the first data slice sequentially at a memory locationof the first one of the plurality of storage zones based on determiningthat the first one of the plurality of storage zones is designated asopen for writes; generating a pointer corresponding to the first dataslice that indicates the first one of the plurality of storage zones andthe memory location, wherein the pointer facilitates retrieval of thefirst data slice in response to a first read request from a requestingentity that indicates the first data slice; determining a zonereallocation requirement at a time after the first data slice iswritten; selecting the second one of the plurality of storage zones tobecome open for writes based on the zone reallocation requirement; anddesignating the second one of the plurality of storage zones as open forwrites in response to selecting the second one of the plurality ofstorage zones based on the zone reallocation requirement.
 22. The methodof claim 21, wherein the first data slice is written sequentially basedon an append point, and wherein the append point is updated after thefirst data slice is written based on a length of the first data slice.23. The method of claim 21, wherein exactly one storage zone is selectedand designated as open for writes based on the zone allocationparameters, wherein the exactly one storage zone is the first one of theplurality of storage zones, and wherein the method further comprises:designating all remaining storage zones of the plurality of storagezones that are not the exactly one storage zone as closed for writes.24. The method of claim 21, further comprising: selecting a first subsetof storage zones to be open for writes from the plurality of storagezones based on the zone allocation parameters, wherein a number ofstorage zones of the first subset of storage zones is selected to be thefixed number of storage zones to be designated as open for writesindicated in the zone allocation parameters, and wherein the firstsubset of storage zones includes the first one of the plurality ofstorage zones and does not include the second one of the plurality ofstorage zones; designating the first subset of storage zones as open forwrites; designating all storage zones in the plurality of storage zonesthat are not included in the first subset of storage zones as closed forwrites; selecting a second subset of storage zones to be open for writesfrom the plurality of storage zones based on the zone reallocationrequirement, wherein the second subset of storage zones includes thesecond one of the plurality of storage zones, wherein the zonereallocation requirement includes a requirement to maintain the fixednumber of storage zones as open for writes, wherein the number ofstorage zones is included in the second subset of storage zones inresponse to the requirement to maintain the fixed number of storagezones as open for writes; and selecting the first one of the pluralityof storage zones to be closed for writes based on selecting the secondone of the plurality of storage zones to be open for writes to meet therequirement to maintain the a fixed number of storage zones as open forwrites.
 25. A method for execution by a storage unit of a dispersedstorage network (DSN) that includes a processor, the method comprises:selecting a first one of a plurality of storage zones of a memory deviceof the storage unit to be open for writes based on zone allocationparameters; selecting a second one of the plurality of storage zones ofa memory device of the storage unit to be closed for writes based on thezone allocation parameters indicating a requirement for exactly a fixednumber of storage zones to be designated as open for writes; designatingthe first one of the plurality of storage zones as open for writes inresponse to selecting the first one of a plurality of storage zones tobe open for writes; receiving, via a network, a first data slice forstorage after designating the first one of the plurality of storagezones as open for writes; writing the first data slice sequentially at amemory location of a first one of a plurality of storage zones based ondetermining that the first one of the plurality of storage zones isdesignated as open for writes; generating a pointer corresponding to thefirst data slice that indicates the first one of the plurality ofstorage zones and the memory location, wherein the pointer facilitatesretrieval of the first data slice in response to a first read requestfrom a requesting entity that indicates the first data slice;determining a zone reallocation requirement at a time after the firstdata slice is written; selecting a the second one of the plurality ofstorage zones to become open for writes based on the zone reallocationrequirement; and designating the second one of the plurality of storagezones as open for writes in response to selecting the second one of theplurality of storage zones based on the zone reallocation requirement.